MIPS: Hugetlb: Keep TLB cache hot while flushing

If we only flush the TLB of the given huge page, the TLB cache remains hot
for the relevant mm as it is, and less will be refilled after flush, huge
or not.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
Cc: linux-mips@linux-mips.org
Acked-by: David Daney <david.daney@cavium.com>
Patchwork: https://patchwork.linux-mips.org/patch/2860/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>